1. Field of the Invention
This invention relates to a process for manufacturing a piece made of composite material with a concave shape, in particular a beam with a U-shaped cross-section. It also relates to a device for its implementation whose purpose is, on the one hand, to ensure a homogeneous impregnation of a fiber preform by injection or infusion of a product that can form a matrix, and, on the other hand, to ensure a good surface condition and an optimal dimensional precision in particular on the level of the outside surface.
1. Description of the Related Art
The pieces made of a composite material comprise a matrix, for example made of resin, reinforced by fibers. According to one widely used embodiment, the fibers come in the form of a fiber preform, with one or more fold(s) that are woven or not.
Prior to the polymerization phase, the product that forms the matrix is to impregnate this preform homogeneously to obtain a piece that has optimal characteristics.
According to a first operating mode, referred to as injection, the product that forms the matrix, generally resin, is injected into the preform at one or more points and even over the entire surface of the preform, optionally with a diffusion medium.
According to another operating mode, referred to as infusion, the product that forms the matrix is integrated in the preform and comes in the form of, for example, one or more inserted resin film(s) or film(s) placed side by side with folds that form said preform.
To implement this impregnation, a device as described in particular in the documents US2004/0219244 or US2005/0031720 and illustrated in FIG. 1 is used.
According to this document, the preform 10 is placed in a first chamber 12 that is delimited by a substrate 14 and a first semi-sealed membrane 16, i.e., permeable to gas but sealed to the product that is able to form the matrix, whereby at least one feed point 18 is provided in said first chamber 12.
In addition, the device comprises a second chamber 20 that is delimited, on the one hand, by a second gas-tight membrane 22, and, on the other hand, by the first semi-sealed membrane 16, whereby said chamber 20 comprises at least one opening 24 for extracting the gases that are contained in said second chamber 20 and thus allow the gases that are present in said first chamber 12 to pass.
The intake of gases into the first chamber 12 brings about the diffusion of the product that is able to form the matrix in the entire preform.
Thus, during the infusion or injection phase, the first semi-sealed membrane 16 ensures an optimum filling and degassing of the preform without drawing in the product that is able to form the matrix.
Sealing means 26 are provided to ensure the seal between the substrate 14 and the first semi-sealed membrane 16 as well as sealing means 28 between the substrate 14 and the second sealed membrane 22.
In addition, a draining fabric 30 can be placed in the second chamber so as to promote the evacuation of gases.
To obtain the smoothing of the surface of the preform that is in contact with the first semi-sealed wall 16, a smoothing plate 32 can be used and placed in the second chamber 20, inserted between the draining fabric and the first semi-sealed wall 16. It also makes it possible to homogenize the pressure forces on the preform.
According to one embodiment, the semi-sealed membrane 16 consists of a microporous fabric, whereby the small diameter of the pores makes possible the passage of gases but blocks the passage of viscous fluids such as the product that is able to form the matrix.
This invention relates more specifically to the manufacturing of beams, used in the aeronautical field, for example at the central section of an aircraft.
According to an operating mode that is illustrated in FIG. 2 for obtaining a beam with a U-shaped cross-section, the same elements as those illustrated in FIG. 1 are used, with the substrate 14 having a U shape that is adapted to the inside face of the U-shaped cross-section. The layers or folds of fibers are draped over the substrate 14 automatically or manually.
Below, the other elements of the device are applied to the U-shaped preform.
This operating mode does not provide satisfaction because it does not make it possible to control the thicknesses and to obtain a satisfactory surface condition at the outside surface (the one that is not in contact with the substrate 14).
Consequently, following the polymerization, it is necessary to correct the geometry of the thus produced piece to assemble it with adjacent pieces. This additional operation leads to increasing the manufacturing cost of the piece and to a loss of resistance because of the breaking of fibers during the geometric correction of the piece.
According to another operating mode that is illustrated in FIG. 3, the piece is made between a mold 14 and a counter-mold 32:
After the draping of the layers or folds of fibers on the substrate 14 that is placed between the branches of the U, the counter-mold 32 is installed.
Even if it makes a better control of the thicknesses possible, this operating mode is not satisfactory because it is necessary to use a counter-mold 32 that does not expand with temperature, for example a carbon-based material, for enabling demolding of the piece, which leads to significantly increasing the cost of the device. Actually, the counter-mold 32 would have a tendency to tighten the piece if it was metal because of a contraction phenomenon during the cooling phase.